Coiled tubing is utilized in numerous field operations related to drilling and maintaining wells. For example, coiled tubing units are often employed in oil and gas wells to perform well unloading, acidizing/stimulation, tool conveyance, well logging, drilling, fracturing, and so forth. Coiled tubing refers to a continuous length of pipe or tubular product that can be wound on a spool. Coiled tubing is typically 1 inch to 4.5 inches in diameter and is used by a coiled tubing unit in field operations for production, maintenance, and intervention. Depending on the tubing diameter and the associated spool size, coiled tubing can range from 2,000 feet to 20,000 feet or greater in length.
Coiled tubing is often used in field operations to perform functions similar to those performed by some wireline systems. Indeed, coiled tubing may be utilized in conjunction with wireline that is disposed within the coiled tubing to facilitate communication with a downhole tool coupled to the coiled tubing, enable the supply of power to downhole monitoring devices, or the like. In contrast to operations that merely utilize wireline, coiled tubing operations involve pushing the coiled tubing into a wellbore rather than relying on gravity to facilitate lowering the wireline into the wellbore. During a typical coiled tubing operation, the coiled tubing is substantially straightened and pushed into a wellbore with an injector header. Further, the injector header is used to retract the coiled tubing from the wellbore by rewinding it onto a storage spool. In certain coiled tubing operations, coiled tubing is extended into a wellbore and rewound multiple times in order to perform maintenance, remove drill cuttings, and so forth.
Many coiled tubing applications include the use of a downhole tool (e.g., any of various tool strings or downhole instruments) connected to the coiled tubing at the downhole end. In some coiled tubing applications, wireline cable is pumped into the coiled tubing, connected to surface equipment, and connected to the downhole tool at the downhole end of the coiled tubing. The physical connection of the downhole tool to the coiled tubing is achieved via a coil connector, which is a downhole device designed for such connections and designed to withstand related functional and environmental stresses. The process of connecting the downhole tool with the coiled tubing and/or the wireline is typically referred to as “heading up” the coiled tubing assembly, which is difficult and time consuming.
For various reasons (e.g., equipment fatigue or accumulation of wireline slack) during a coiled tubing operation, it often becomes necessary or desirable to rehead the coiled tubing. In other words, it becomes necessary to disconnect the downhole tool from the downhole end of the coiled tubing and/or wireline and then head up the coiled tubing again (i.e., reconnect the downhole tool to the coiled tubing and/or the wireline). This requires the inconvenient tasks of pulling the coiled tubing from the wellbore, removing the downhole tool, and reattaching the downhole tool to the coiled tubing assembly. Also, this generally includes cutting the coiled tubing, performing certain maintenance issues (e.g., repositioning the wireline), and so forth. It is now recognized that reheading the coiled tubing may be performed more frequently than necessary because the level of equipment fatigue, accumulated wireline slack, or the like is unknown.